Flat-shaped hollow bodies of this type utilized in ventilation or drainage panels or mats or used as heat exchanger plates or panels for absorbers or for floor heating units, are known on the basis of German Offenlegungsschrift No. 25 21 374. Such flat-shaped hollow bodies are formed by welding together, or glueing together, deep drawn plates. This type of fabrication is extremely costly and only possible when practiced on a discontinuous basis.
On the basis of German Offenlegungsschrift No. 22 10 445, a process is known in which a thermoplastic insulating foil, having a large number of gas-filled cells for use as packing material or heat insulation material, can be fabricated in a continuous mode from a thermoplastic hose of extremely thin wall thickness. This can be accomplished in a device consisting of two drivable drums, which rotate in opposing directions and which have appropriate recesses in their surface areas conforming to the cells, and to which a vacuum can be applied from the inside of the drums. Such an apparatus can manufacture only very thin-walled foils having a wall thickness of 0.1-0.2 millimeters, since the hose stock cannot be cooled after the forming but while it is still in the space between the drums. Such a device is not suitable for the manufacture of flat-shaped hollow bodies having a wall thickness of even a few tenths of a millimeter.